1. Field of the Invention
The present invention relates to a construction technique for a trochoid pump applicable in a fuel injection pump, in a fuel injection device of a diesel engine.
2. Related Art
Conventionally, there are well-known trochoid pumps. For example, as described in JP 2002-98065, a trochoid pump, which is applicable as a fuel injection pump in a fuel injection device of a diesel engine, is disclosed. The diesel engine needs to pressurize fuel at high pressure and inject them so as to deliver them into the air compressed at high pressure in a combustion chamber. The fuel injection device assumes pressurizing and sending fuel. The fuel injection device includes the fuel injection pump that pressurizes fuel at high pressure and sends them into injection nozzles, as well as injection nozzles that inject fuel into cylinders.
The prior art on a trochoid pump 200 will be described with reference to FIG. 14 as a cross-sectional view showing a simplified cross section. The trochoid pump 200 is covered with a casing 206 and a removable cap 205, and an inner rotor 201 and an outer rotor 202 are rotatably provided therein.
A drive gear 207 as a bevel gear is annealed and fixed into, or pressed into one end of a driving shaft 203. The other end of the driving shaft 203 is penetrated into the central portion of the inner rotor 201 and supported in the cap 205. A rotational direction of the inner rotor 201 is regulated by a drive pin 218.
A camshaft 209 is driven via the gear by a crankshaft (not shown) and it vertically moves a plunger (not shown) by rotating a cam (not shown) formed on the camshaft 209 and rotates the drive gear 208. In this regard, the camshaft 209 drives the driving shaft 203 via the bevel gear composed of the drive gears 207, 208.
Due to the above-mentioned construction, as the inner rotor 201 is driven by the camshaft 209, the outer rotor 202 is rotated. Because the centers of the inner rotor 201 and the outer rotor 202 are decentered and the number of teeth of the inner rotor 201 are one less than the number of teeth of the outer rotor 202, the fuel oil is interposed between the rotors 201 and 202 and is delivered from an inlet port (not shown) to an outlet port (not shown).
Due to the above-mentioned construction of the trochoid pump 200, the driving shaft 203 is regulated by the cap 205 and the drive gear 208 in a thrust direction (in a direction of arrow in FIG. 10).
However, when the drive gear 208 as the bevel gear is abraded, the driving shaft 203 is offset in the thrust direction, thereby increasing a backlash (a gap when the gears are enmeshed). The more the backlash increases, the more the abrasion of the drive gears 207 and 208 increase, thereby shortening the life cycle of a product.
The problem so as to be solved is to prevent the offset of the driving shaft in the thrust direction in the trochoid pump.